This phase IV open-label protocol will determine the changes in weight, body composition, resting energy expenditure (REE), viral load, and CD4 + T-cell counts in HIV-infected patients receiving AZT/3TC (Combivir) and a protease inhibitor or a non-nucleoside analog. Thirty patients will be studied at New England Medical Center Hospitals, in Boston. Outpatients either naive to antiretroviral therapy, or needing a change of their current regimen and with no ongoing opportunistic infections will be eligible. After signing informed consent, patients will have a baseline visit, and follow up visits every 2 months for 6 months. Medical history, physical examination, adherance, failure of therapy and/or in tolerance will be assessed, and measurements of weight, body composition by bioelectric impedance and dual x-rays absorptiometry, REE, and blood tests will be performed at each visit. The primary end-point analysis will be made at 6 months.